1. Field of the Invention
This invention relates to a method of measuring distortion and device for transmitting beam or a three-dimensional surface shape of a measured body.
2. Discussion of Background
Conventionally, as a method of measuring distortion of a transmitting beam or a three-dimensional surface shape of a glass plate or the like using a light beam, a method has been proposed wherein a transparent board with a black lattice pattern on its surface is disposed between a light source and a measured body, a transmitting image or a reflecting image of the lattice pattern is projected on a screen, and the distortion of the pattern is measured by optically observing the distortion of the pattern or by taking a photograph thereof followed by optical observation, either one of which is a general practice. However, in this method, a measurement error is apt to be caused by each individual measuring person. Furthermore, it is extremely inconvenient in view of the automation of the measurement.
Explanation will be given of the conventional measuring method taking an example of measuring the distortion of a transmitting beam. FIG. 6 is a conceptual diagram showing the conventional method.
Beam 11 is radiated on a measured body 12 such as a glass plate through a transparent meshed board 9 with a lattice having mesh intervals of 15 mm to 50 mm, and a lattice image formed by the transmitting beam is taken by a camera 13. By using an enlarged photograph obtained as above, deviation (inclination) of the lattice image with respect to a reference line is measured an is determined to be a quantity of the distortion of the transmitting beam. There also is a case wherein an operator performs optical observation by projecting a transmitting image of the lattice rather than taking the lattice image by a camera.
However, in such a method, since the deviation of the lattice image from the reference line is measured by the inclination, an extremely accurate reference line is required. Since the measurement is finally performed by optical observation, a dispersion of the measurement value is considerable depending on the observer, and therefore the accuracy is not sufficient. Furthermore, much time is required for the inspection.
A glass plate for an automobile is often provided with a small radius of curvature. Accordingly, to project the meshed image over a total surface of the glass plate, an extremely large screen or a surrounding screen is required. Therefore, size of the measuring the device is undesirably magnified.
This representation of the distortion by the inclination is not necessarily fitted to an actual observation. Even if the inclination of the surface of the glass plate is deviated from that of a reference value, so far as the surface is smooth, often the deviation is not a problem when a person actually observes the transmitting beam.
As a trial of reducing the inaccuracy of the measurement of the distortion of a transmitting beam by optical observation, a method is proposed in Japanese Unexamined Patent Publication No. 129142/1989 wherein a plate glass is intermittently rotated and a laser beam is radiated thereon, thereby calculating a refracting power of a specified point of the glass plate, which is determined to be the distortion of the transmitting beam.
However, in this method wherein the laser beam having a strong directivity is radiated directly on the glass plate, the measurement of the distortion of transmitting beam of the glass plate is performed only with respect to a specified point. Therefore, to measure the distortion of transmitting beam over the whole surface of the glass plate, a number of laser devices and beam receiving devices are required whereby the integrated device is magnified and expensive.
The applicant proposes to achieve the automation of the inspection removing the difference in the measurement error by each individual measuring person by measuring an incident direction of a beam which is emitted from a bright spot on a screen formed by radiating a laser beam or the like on the screen, and reflected by a measured body (Japanese unexamined Patent Publication No. 44504/1991). In this case, a beam receiving device is often utilized which is provided with a beam receiving plane composed of a great number of pixels such as a CCD camera or a video camera, since the scope thereof for receiving the transmitting beam or the reflecting beam is wide, which is suitable for efficient performance of the measurement.
However, when the measurement is performed on a measured body having a surface area of about several square meters such as a windshield glass for an automobile, time of several tens to about one hundred hours is required even by this method, since the beam receiving device such as a CCD camera or a video camera cannot detect the incident direction with an accuracy smaller than the size of a pixel. Thus, in measuring the distortion of a transmitting beam or a shape thereof with a required accuracy, the scope measurable by a single beam receiving device is extremely limited.